This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for operating gas turbine engines.
Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high-pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low-pressure compressor, or booster, for supplying compressed air to the high-pressure compressor.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from at least some gas turbines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC & CO).
Accordingly, at least one known gas turbine engine includes a water injection system that is configured to inject water into the combustor to facilitate reducing nitrous oxide emissions from the gas turbine engine by reducing the flame temperature in the combustor. However, injecting water into the combustor may also result in a significant decrease in the fuel efficiency of the gas turbine engine.